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Fig. 5 ASS1 deficiency is associated with a specific neuronal differentiation defect. At the 1-cell stage, wildtype or transgenic zebrafish larvae [tg(elavl3:eGFP) or tg(NBT/lyn:eGFP)] were either injected with ASS1-targeting MO or mock and subjected to ISH applying the indicated probes for mRNA detection (A-B, E-F) or in vivo imaging using a binocular fluorescence microscope (Csingle bondD, MZ16F, Leica) at 1 or 3 dpf. Lateral view with anterior to the left (A-F). ASS1-deficient zebrafish larvae exhibited reduced expression of pro-neuronal markers neurod1 and elavl3 at 1 and 3 dpf (A, B). Analogously, MO-injected transgenic zebrafish larvae expressing eGFP under control of the elavl3 promoter showed almost absent eGFP-expression at 1 dpf, which was partially restored at 3 dpf (C). However, ASS1-deficient tg(NBT/lyn:eGFP) transgenic zebrafish exhibited constantly reduced neuronal eGFP expression until 3 dpf as indicator of reduced neuronal cell mass (D). In contrast, glial cell markers gfap (astrocytes) and olig2 (oligodendrocytes) remained unchanged in response to ASS1 deficiency when compared to wildtype control (E, F). Important ISH-staining patterns are marked with arrow head(s) in the wildtype and MO-treated cohort (A, B, E, F). Distinct GFP-expression patterns of the transgenic tg(elavl3:eGFP) (C) or tg(NBT/lyn:eGFP) (D) zebrafish strains are marked with an asterisk in both cohorts.